On Tue, Feb 10, 2015 at 04:22:50PM -0800, Alexei Starovoitov wrote: > >> not all tools use libtraceevent. > >> gdb calls perf_event_open directly: > >> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/nat/linux-btrace.c > >> and parses PERF_RECORD_SAMPLE as a binary. > >> In this case it's branch records, but I think we never said anywhere > >> that PERF_SAMPLE_IP | PERF_SAMPLE_ADDR should come > >> in this particular order. > > > > What particular order? Note, that's a hardware event, not a software > > one. > > yes, but gdb assumes that 'u64 ip' precedes, 'u64 addr' > when attr.sample_type = IP | ADDR whereas this is an > internal order of 'if' statements inside perf_output_sample()...
This is indeed promised in the data layout description in include/uapi/linux/perf_event.h. There is no other way to find where fields are; perf relies on predetermined order of fields coupled with the requested field bitmask. So we promise the order: id, ip, pid, tid, time, addr,.. etc. So if you request IP and ADDR but none of the other fields, then you know your sample will start with IP and then contain ADDR. The traceevent thing has a debug/trace-fs format description of fields that is supposed to be used. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
